Why not just ask him? Compose an email with all your actual questions. If there's something you've tried to solve the problem or learn about it yourself, include that. A senior is there to mentor junior developers as well as take on their backlogs. It's terrific that you want to respect his time, and if you come prepared with questions, ready to learn he's likely to respect you for that. Find some times on his calendar that you think will work, and make sure you're ready all the way.

Outside of hours isn't out the question, but it's also not the kind of respect you seem to think it is. I prefer that these things happen during business hours so as not to affect people's life schedules.

Don't be afraid to ask. Be prepared to learn. Be prepared for suggestions on timing, and be flexible on letting it happen. You won't learn if you don't ask.

Why not just ask him? Compose an email with all your actual questions. If there's something you've tried to solve the problem or learn about it yourself, include that. A senior is there to mentor junior developers as well as take on their backlog. It's terrific that you want to respect his time, and if you come prepared with questions, ready to learn he's likely to respect you for that. Find some times on his calendar that you think will work, and make sure you're ready all the way.

Outside of hours isn't out the question, but it's also not the kind of respect you seem to think it is. I prefer that these things happen during business hours so as not to affect people's life schedules.

Don't be afraid to ask. Be prepared to learn. Be prepared for suggestions on timing, and be flexible on letting it happen. You won't learn if you don't ask.